SpectroMaster® Product brochure
SpectroMaster®
Goniometer-Spectrometer for determination of the refractive index
SpectroMaster® Goniometer-Spectrometers are employed by optical glass manufacturers, national metrology institutes as well as scientific research institutes with highest accuracy demands for the determination of the refractive index and dispersion of optical glass and crystalline materials in the UV, VIS or IR spectral range.
High precision refractive index determination
The SpectroMaster® HR 600 Goniometer-Spectrometer is the most accurate refractive index measurement system currently on the market. With an accuracy of 2×10⁻⁶ it is the industry leader in terms of high-precision determination of the refractive index.
Wide wavelength range
Traceable to international standards
Product Overview
SpectroMaster® 600 HR
Automated Precision-Goniometer-Spectrometer
The SpectroMaster® 600 HR is the most accurate refractive index measurement system currently on the market.
This accuracy is the result of ultra-high precision components like the motorized air bearing rotary table or the high-class mirror optics and the high-quality manufacturing including careful inspection of all relevant parameters. The motorized goniometer is equipped with backlash-free piezo motors of negligible power dissipation for optimum thermal stability.
SpectroMaster® 600 MAN
Manual precision Goniometer-Spectrometer
The SpectroMaster® 600 MAN works with mirror optics and thus retains the advantage that the collimator and autocollimator do not have to be refocused over the entire measurable spectral range. The lamp change wheel, goniometer and sample table can be operated manually and the user is guided through the measurement procedure with software support. The measurement system achieves excellent accuracy in refractive index measurement and is therefore an alternative to the fully automated SpectroMaster® 600 HR with lower requirements in the measurable spectral range and measurement speed.
SpectroMaster® 300 MAN
Manual precision Goniometer-Spectrometer
The SpectroMaster® 300 MAN uses refractive optics. The high accuracy of this instrument is achieved by special focusing optics, so that the telescope and the collimator are focused to best collimation at the specific measurement wavelength. It offers a very high system accuracy for refractive index measurement.
Software
SpectroMaster® Software
The complete functionality of the SpectroMaster® instrument is controlled by an integrated Windows 7 based software program.
It processes the measured values from autocollimator and high-precision angle encoder to an exact measured value for the refractive index.
With the motorized SpectroMaster® 600 HR, measurements can be performed fully automatically over the complete spectral range. If an approximation for the refractive index of a certain glass type is known, the software searches and automatically measures each programmed spectral line and gives a report on the measured refractive indices. The initial approximation for the refractive index can either be entered manually by the user or calculated by the software via an integrated glass database from stored dispersion coefficients. Additionally, sophisticated tools enable the quick and easy characterization of unknown glass types, so that accurate refractive index data can be obtained in a few minutes. Of course, the software corrects the measurement data to take into account the ambient air refractive index depending on temperature, humidity and pressure.
Technical Data
| Parameter | SpectroMaster® 600 HR | SpectroMaster® 600 MAN | SpectroMaster® 300 MAN |
|---|---|---|---|
| Max. measurable wavelength range. Specific wavelengths are discrete and depend on the chosen light source | 195 nm … 12000 nm | 365 nm … 1014 nm | 365 nm … 1014 nm |
| Standard measurable wavelength range. Specific wavelengths are discrete and depend on the chosen light source | 365 nm … 1014 nm | 365 nm … 1014 nm | 405 nm … 643 nm |
| Optional measurable wavelength range. Specific wavelengths are discrete and depend on the chosen light source | UV: 195 nm … 365 mm | -- | UV: 365 nm |
| SWIR: 1014 nm … 2325 nm | NIR: 1014 nm | ||
| MWIR / LWIR: 4000 nm … 12000 nm | |||
| Apex angle measurement accuracy 1 | ± 0.2 arcsec | ± 0.4 arcsec | ± 0.5 arcsec |
| Refractive index measurement accuracy 1 | ± 2∙10-6 | ± 4∙10-6 | ± 5∙10-6 |
| Refractive index measurement repeatability (1σ) | |||
| UV: 195 nm … 365 mm 2 | 3∙10-6 | -- | -- |
| VIS / NIR: 365 nm … 1014 nm | 1∙10-6 | 1∙10-6 | 1∙10-6 |
| SWIR: 1014 nm … 2325 nm 3 | 5∙10-6 | -- | -- |
| MWIR / LWIR: 4000 nm … 12000 nm 4 | 1∙10-4 | -- | -- |
1) Accuracy is traceable to national standards and repeatability is demonstrated by measurement of a certified reference prism (material N-BK7, homogeneity H4, apex angle 65°, aperture Ø30mm, surface quality λ/10) at the following wavelengths: 404.6 / 435.8 / 479.9 / 508.6 / 546.1 and 643.8 nm.
Compliance with the above specifications requires optimum and stable environmental conditions in terms of temperature (±0.1°C), humidity (50-70%), pressure (±0.5 hPa) and airflow, high surface quality of the specimen (< λ/10) and an aperture of not less than Ø30 mm. We also recommend the “Meteo Station 5-400-030” as an accessory for monitoring ambient conditions.
2) Verified at the wavelengths 312 and 365 nm with a reference specimen (material quartz glass, tip angle 65°, aperture Ø30 mm).
3) Verification at the wavelengths 1014 and 1530 nm with a reference specimen (material N-BK7, tip angle 65°, aperture Ø30 mm).
4)Verification at a wavelength in the specified range with a reference specimen (material ZnSe, tip angle 20°, aperture Ø20 mm).
Knowledge Base
Measurement Principle
Minimum deviation method
The minimum deviation method as described by Fraunhofer at the beginning of the 19th century is sketched below. It is based on the refraction of light by a precise prism manufactured from the optical material under investigation. A bundle of monochromatic collimated light from a collimator enters at one surface of the prism and is refracted at a certain deviation angle δ when leaving the second surface. The deviation angle is a function of the wavelength λ and is measured by a telescope attached to a goniometer table. The angle enclosed by the two prism surfaces is generally called the apex angle α of the prism. When the incidence angle θ at which the light enters the prism is changed, the deviation angle δ changes too. It can be shown that the deviation angle δ becomes minimal when the angle θ’ at which the beam leaves the second surface is equal to θ, i.e. θ = θ’. This symmetric case is the so-called minimum deviation condition. In this case, the index of refraction of the prism material can be calculated according to
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Where nair is the refractive index of the ambient air. nair is a function of the wavelength λ, temperature T, pressure p and humidity and can be calculated with sufficient accuracy from p and T with the generally approved Edlén equation. In most cases, the humidity can be neglect- ed. Since these calculations are quite complex and error-prone, this is done automatically by the instrument software.
The refractive index can be determined only when the apex angle α is precisely known. Both angles α and δ are measured with an ultra-precision goniometer with sub-arcsecond accuracy. The apex angle α is measured with an autocollimator attached to the goniometer table.
